1. Field of Invention
The present invention relates to an ink-jet head for printing by ejecting ink onto a print medium, and to an ink-jet printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink, which is supplied from an ink tank, to pressure chambers. The ink-jet head selectively applies pressure to each pressure chamber to eject ink through a nozzle. As a means for selectively applying pressure to the pressure chambers, an actuator unit may be used in which ceramic piezoelectric sheets are laminated.
As an example, the previously described ink-jet head is known to have one actuator unit in which continuous flat piezoelectric sheets extending over a plurality of pressure chambers are laminated. At least one of the piezoelectric sheets is sandwiched by an electrode common to many of the plurality of pressure chambers that is being kept at the ground potential, and many individual electrodes, i.e., driving electrodes, disposed at positions corresponding to the respective pressure chambers. The part of the piezoelectric sheet being sandwiched by the individual and common electrodes and polarized in its thickness, is expanded or contracted in its thickness direction as an active layer, by the so-called longitudinal piezoelectric effect, when a individual electrode on one face of the sheet is set at a different potential from the potential of the common electrode on the other face. Thereby, the volume of the corresponding pressure chamber changes, so ink can be ejected toward a print medium through a nozzle communicating with the pressure chamber.
Recently, in such an ink-jet head as described above, it has been strongly desired to drive the actuator unit with a low voltage in order to reduce power consumption and manufacturing cost. However, any existing ink-jet head, as described above, could not sufficiently meet the request.